Urinary tract infection (UTI) commonly occurs among young, otherwise healthy women in their sexually active years, and accounts for 3% of all physician visits in this group. Our overall goal is to demonstrate that UTI can be transmitted between sex partners, and that transmittable uropathogens are associated with unique, identifiable characteristics. We will identify behavioral and bacterial factors associated with transmission of UTI, by comparing the degree of concordance of urinary isolates from 500 women with UTI and the urethral flora of their male sex partners to the degree of concordance amont 500 controls and their sex partners by the presence of behavioral characteristics and for E. coli, virulence signatures. By comparing the virulence signatures of paired E. coli urinary isolates to fecal isolates from UTI cases, and comparing virulence signatures from E. coli isolates from UTI cases to isolates form controls, we will be able to identify factors characteristic of uropathogens. Specifically we plan to: Aim 1. Demonstrate heterosexual transmission of uropathogens. Aim 2. Identify bacterial virulence characteristics associated with transmission of E. coli between partners. Aim 3. Identify bacterial virulence characteristics associated with the development of UTI, by comparing the virulence signatures of E. coli from the urine of women with UTI to virulence signatures o E. coli from their fecal flora, E. coli from their sex partners' urine E. coli from the urine or vagina of controls, and E. Coli from the urine of sex partners of controls. The identification of heterosexually transmitted UTI and the distinct characteristics of uropathogens has implication for prevention, treatment, and understanding of the epidemiology of all UTI. These include vaccine development, treatment of sex partners, and increased ability to detect preventable risk factors.